Tuning the Optical Band Gap of Semiconductor Nanocomposites—A Case Study with ZnS/Carbon

Abstract

The linear photochemical response of materials depends on two critical parameters: the size of the optical band gap determines the onset of optical excitation, whereas the absolute energetic positions of the band edges define the reductive or oxidative character of photo-generated electrons and holes. Tuning these characteristics is necessary for many potential applications and can be achieved through changes in the bulk composition or particle size, adjustment of the surface chemistry or the application of electrostatic fields. In this contribution the influence of surface chemistry and fields is investigated systematically with the help of standard DFT calculations for a typical case, namely composites prepared from ZnS quantum dots and functionalized carbon nanotubes. After comparing results with existing qualitative and quantitative experimental data, it is shown conclusively, that the details of the surface chemistry (especially defects) in combination with electrostatic fields have the largest influence. In conclusion, the development of novel or improved photoresponsive materials therefore will have to integrate a careful analysis of the interplay between surface chemistry, surface charges and interaction with the material environment or substrate.

Ternary Chalcogenide-Based Quantum Dots and Carbon Nanotubes: Establishing a Toolbox for Controlled Formation of Nanocomposites

“…Therefore, at a relatively low computational cost, the strong on-site Coulombic interaction of localized electrons, which is insufficiently described by LDA or GGA is corrected by an additional Hubbard-like term (Hubbard U parameter). Analogous to our previous studies, 74 the values for the U parameters were obtained semiempirically (see Figure S12 ) and were 4.8 eV for S, 4.5 eV for Se, 9.1 eV for Zn, 6.8 eV for Cu, 8.1 eV for In, and 9.8 eV for Ga. The improvement from the standard GGA calculations toward more accurate results with GGA + U calculations is represented in the Supporting Information (see Table S2 and also see Figures S13 and S14 ).…”

“…This observation is different from our previous studies on electric fields on ZnS QDs, and we would expect that the maximum of the band gap for perfectly passivated nanostructures is centered at E⃗ (z) = 0. 74 This however is in contrast to the computational results, which means that the surfaces of the calculated nanostructures have a nonvanishing dipole density (like in our mentioned previous studies, ZnS with surface defects). Probably this is the result of the unpreventable asymmetric distribution of surface atoms in ternary materials when two opposing surfaces are compared.…”

ZnS Quantum Dots Decorated on One-Dimensional Scaffold of MWCNT/PANI Conducting Nanocomposite as an Anode for Enzymatic Biofuel Cell

“…It has been reported that the combination of ZnS nanoparticles and carbon nanotubes decreased the bandgap of ZnS nanoparticles and increased the conductivity of the several composite folds by providing the passage for better electron transport [ 33 ]. Moreover, the size of the ZnS quantum dots can easily be tuned by the method of preparation, reaction parameters (processing time, temperature), nature, and amount of dopant used.…”

Physical Modifications and Algorithmic Predictions behind Further Advancing 2D Water Splitting Photocatalyst: An Overview

“…Tunning such property can be possible by changing the material composition and particle size, modifying the surface chemistry, or exploiting electrostatic fields. [20] Some highly active catalysts are either confined in specific dimensions or designed differently to be available to reactant molecules to increase catalytic activity. Some physical parameters even can be changed to alter the catalytic property.…”